This application is based on Japanese Patent Application No. 2001-65961 filed on Mar. 9, 2001 the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an apparatus for controlling a catalyst temperature of an engine and a method for controlling the catalyst temperature of the engine. More specifically, the present invention provides a transitional control between a rapid heating control and a normal control of the catalyst temperature.
2. Description of Related Art
The Japanese patent JP-B2-2929895 discloses a rapid heating control for a catalyst of an engine. In this control, ignition timing is retarded to increase an exhaust temperature, and an opening degree of an idle speed control valve (ISC valve) is widened to increase an engine speed. According to the control, since the retarded ignition timing prevents a rough idle, the catalyst is rapidly warmed up without the rough idle. Then, the control is quickly switched to a normal control for maintaining the catalyst temperature within an activated range.
In order to speed up a warm-up of the catalyst, it is proposed to increase a retarding degree of the ignition timing. However, the large retarding degree requires a large advancing change of the ignition timing that may cause a sudden torque-up when the rapid heating control is completed. Although the opening degree of the ISC valve should be decreased when the rapid heating control is completed, decreasing an intake air is not sufficient to suppress the torque-up caused by the ignition timing change since an air system of the engine usually has a greater delay in comparison to the ignition system. Further, relatively large amount of fuel is adhered on an intake passage and cylinders, hereinafter referred to as wet fuel or wet amount of fuel, during a cold starting of the engine where the rapid heating control is necessary. Therefore, an exhaust emission may get worse when the rapid heating control is completed since the wet fuel is introduced into the cylinders by an increased intake air.
It is an object of the present invention to provide an apparatus and a method which are capable of preventing the torque shock when the rapid heating control is completed.
It is another object of the present invention to provide an apparatus and a method which and a method which is capable of preventing the torque shock and lowering the exhaust emission when the rapid heating control is completed.
According to an embodiment of the present invention, an intake air amount is gradually changed from an increased amount under a rapid heating control to a normal amount under a normal control in a direction to decrease an engine torque. Simultaneously, ignition timing is also gradually changed from a retarded ignition timing under the rapid heating control to a normal ignition timing under the normal control in a direction to increase the engine torque. Therefore, the engine is smoothly operated without a torque shock, and is prevented from an emission caused by a sudden increase of fuel amount introduced by the sudden increased airflow.
It is preferable to provide a delay between the beginning of the intake air change and the beginning of the ignition timing change. The delay approaches a relatively quick engine response to the ignition timing and a relatively slow engine response to the intake air. Therefore, it is possible to reduce the torque shock.